Fix 934

[kapedalex]

Description

Fixed bfloat16 eigenvalue crashes by promoting matrices to float32 for numerical stability and updated return type hints to Complex to resolve jaxtyping validation errors.

Fixes #934

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have not rewritten tests relating to key interfaces which would affect backward compatibility